The process according to the invention applies more particularly to the separation of the unconverted HF present in mixtures originating from the manufacture of F133a by fluorination of trichloroethylene or of symmetrical or unsymmetrical tetrachloroethane. For economic reasons, HF must be recovered in anhydrous form to allow it to be recycled to the fluorination reactor.
Various techniques for performing this separation of HF and chlorofluorohydrocarbons have already been described. There may be mentioned, for example:
U.S. Pat. No. 2,640,086, which relates to the separation of HF and of chlorodifluoromethane and employs chloroform to promote the separation into two phases, an HF-rich phase and an HF-poor phase;
U.S. Pat. No. 3,873,629, relating to a continuous process for the separation of HF and of chlorodifluoromethane and consisting in bringing the gaseous mixture of the two constituents into counter-currentwise contact with sulphuric acid;
U.S. Pat. No. 3,976,447, which proposes a separation of HF from gaseous effluents by absorption-desorption on calcium, barium or strontium chloride particles;
U.S. Pat. No. 4,209,470, which describes a process for separating HF from its mixtures with 1-chloro-1,1-difluoroethane, in which, to improve the phase separation, an auxiliary liquid is added, consisting wholly or predominantly of 1,1-dichloro-1-fluoroethane;
patent application No. EP 0,353,970, relating to the separation of HF from its mixtures with 2,2-dichloro-1,1,1-trifluoroethane and/or 2-chloro-1,1,1,2-tetrafluoroethane by phase separation and distillation.
In the case of mixtures of HF and F133a, a simple distillation does not enable them to be separated because HF and F133a form an azeotrope which is more volatile than HF or F133a; the HF content of this azeotrope is approximately 60 mol % (20% by weight). There are no data in the literature on the phase separation of mixtures of HF and F133a; at room temperature and whatever the HF and F133a concentrations, mixtures of HF and F133a do not separate into two phases.